Simulation of Ground-Water Flow and Evaluation of Water-Management Alternatives in the Assabet River Basin, Eastern Massachusetts pptx

88 Appendix 1: Estimated Average Monthly Streamflow, Nonstorm Streamflow, and Model-Calculated Average Monthly Nonstorm Streamflow at Measurement Sites in the Assabet River Basin, Easter

Simulation of Ground-Water Flow and Evaluation of Water-Management

Alternatives in the Assabet River Basin, Eastern Massachusetts

By Leslie A DeSimone

In cooperation with the

Massachusetts Department of Conservation and Recreation

Scientific Investigations Report 2004-5114

U.S Department of the Interior

U.S Geological Survey

Gale A Norton, Secretary

U.S Geological Survey

Charles G Groat, Director

U.S Geological Survey, Reston, Virginia: 2004

For sale by U.S Geological Survey, Information Services

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Suggested citation:

DeSimone, L.A., 2004, Simulation of ground-water flow and evaluation of water-management alternatives in the Assabet River Basin, eastern Massachusetts: U.S Geological Survey Scientific Investigations Report 2004-5114, 133 p

Abstract 1

Introduction 2

Purpose and Scope 4

Description of the Study Area 4

Previous Studies 4

Ground- and Surface-Water Resources 5

Geologic Setting 5

Hydraulic Properties 7

Ground-Water Flow 10

Recharge 10

Water Levels 11

Surface Water 17

Streamflow 17

Ponds and Wetlands 20

Water Use and Management 22

Water Supply and Consumptive Use 24

Wastewater Discharge and Return Flow 32

Simulation of Ground-Water Flow 33

Steady-State Numerical Model 33

Spatial Discretization 33

Boundary Conditions 33

Stresses 36

Recharge and Evapotranspiration 36

Water Withdrawals and Discharges 37

Hydraulic Properties 37

Model Calibration 40

Model-Calculated Water Budgets and Flows 45

Transient Numerical Model 46

Temporal Discretization and Initial Conditions 46

Boundary Conditions and Stresses 49

Hydraulic Properties 50

Model Calibration 50

Model-Calculated Water Budgets and Flows 58

Model Limitations 65

Evaluation of Ground-Water-Management Alternatives 66

Simulation of Altered Withdrawals and Discharges 66

Simulation of No Water Management 66

Simulation of Increased Withdrawals and Discharges 69

Simulation of Ground-Water Discharge of Wastewater 72

Hypothetical Discharge Site in the Fort Meadow Brook Subbasin 76

Hypothetical Discharge Site in the Taylor Brook Subbasin 77

Hypothetical Discharge Site in the Cold Harbor and Howard Brooks Subbasins 77

Hypothetical Discharge Site in the Stirrup Brook Subbasin 78

Summary of Scenarios of Ground-Water Discharge of Wastewater 78

Simulation-Optimization of Withdrawals, Discharges, and Streamflow Depletion 78

Methods 79

Simulation-Optimization of Withdrawals and Discharges in Westborough 79

Response Coefficients 79

Management-Model Application 81

Summary 85

Acknowledgments 88

References 88

Appendix 1: Estimated Average Monthly Streamflow, Nonstorm Streamflow, and Model-Calculated Average Monthly Nonstorm Streamflow at Measurement Sites in the Assabet River Basin, Eastern Massachusetts 95

Appendix 2: Model-Calculated Average Annual, March, and September Hydrologic Budgets for Subbasins in the Assabet River Basin, Eastern Massachusetts 105

Appendix 3: Average Monthly Withdrawals and Discharges at Permitted Municipal and Nonmunicipal Water-Supply Sources and Wastewater-Treatment Facilities used in the Calibrated Transient Model to Simulate Average 1997–2001 Conditions and in a Scenario of Increased Withdrawals and Discharges in the Assabet River Basin, Eastern Massachusetts 125

Figures 1–3 Maps showing: 1 The Assabet River Basin, subbasins, streamflow-gaging stations, and long-term observation well, eastern Massachusetts 3

2 Surficial geology of the Assabet River Basin 6

3 Depth-weighted hydraulic conductivity from well logs and transmissivity zones in stratified glacial deposits in the Assabet River Basin 9

4, 5 Graphs showing: 4 Monthly mean precipitation for long-term average conditions and for 1997–2002 at National Oceanic and Atmospheric Administration weather stations in Bedford and West Medway 12

5 Monthly recharge rates estimated from A, streamflow records at the Assabet River streamflow-gaging station in Maynard; B, streamflow records at the Nashoba Brook streamflow-gaging station; and C, climate data from Bedford and West Medway weather stations, for long-term average conditions and 1997–2001 12

6 Map showing streamflow-measurement sites, observation wells, and pond- measurement sites in the Assabet River Basin 13

7–12 Graphs showing: 7 Monthly and daily average water levels at long-term observation well ACW158, Assabet River Basin 15

8 Measured water levels, September 2001 through December 2002, and estimated average monthly water levels, 1997–2001, at selected observation wells in the Assabet River Basin 16

9 Monthly mean streamflow for long-term average conditions and daily mean streamflow, 1997–2001: A, Assabet River streamflow-gaging station at Maynard; B, Nashoba Brook streamflow-gaging station near Acton 20

10 Instantaneous streamflow measurements, June 2001 through December 2002,

and estimated mean monthly streamflow and nonstorm streamflow at selected

flow-measurement sites in the Assabet River Basin 21

11 Measured water levels, September 2001 through December 2002, at selected

ponds and impoundments in the Assabet River Basin .22

12 Schematic diagram showing water use and return flows in the Assabet River

Basin .23

13, 14 Maps showing:

13 Public-water and sewer systems in the Assabet River Basin 26

14 Permitted water-supply withdrawals and wastewater discharges in the

Assabet River Basin 29

15 Graph showing monthly average permitted withdrawals, wastewater discharges,

and imported water for public supply, 1997–2001, in the Assabet River Basin 30

16, 17 Maps showing:

16 Areas of private-water supply with consumptive water use and areas of

public-water supply with septic-system return flow in the Assabet River

Basin .31

17 Model area, grid, hydraulic conductivity zones, and simulated ponds, streams,

water withdrawals and surface-water inflows for ground-water-flow models

of the Assabet River Basin 34

18 Diagram showing vertical discretization for ground-water-flow models of the

Assabet River Basin 35

19 Relation between observed and model-calculated A, ground-water levels; and

B, nonstorm streamflow for average conditions, 1997–2001, for the steady-state

ground-water-flow model of the Assabet River Basin .43

20 Map showing model-calculated steady-state water table in the Assabet River

Basin 44

21 Graph showing model-calculated average annual inflows to and outflows from

the surficial layer of the simulated ground-water-flow system in subbasins of the

Assabet River Main Stem and tributary subbasins, 1997–2001, Assabet River Basin 46

22 Map showing anthropogenic outflows relative to total model-calculated average

A, annual; and B, September outflows from the simulated ground-water-flow

system in subbasins of the Assabet River Basin 47

23, 34 Graphs showing:

23 Model-calculated components of average annual nonstorm streamflow in

subbasins of the Assabet River Main Stem, 1997–2001 .48

24 Model-calculated average annual total nonstorm streamflow and the

component of flow that originated as wastewater, for existing conditions

and two hypothetical scenarios of altered withdrawals and discharges in

the Assabet River Basin .48

25 Monthly average recharge rates and rates of evaporative loss of ground

water for the transient ground-water-flow model of the Assabet River Basin 49

26 Model-calculated and observed water-level fluctuations during the average annual

cycle for selected observation wells and ponds in the Assabet River Basin .51

27 Model-calculated and observed mean monthly nonstorm streamflow at the

A, Assabet River at Maynard; and B, Nashoba Brook near Acton streamflow-gaging

stations on the Assabet River, Assabet River Basin 52

28 Model-calculated and observed mean monthly nonstorm streamflow at flow-

measurement sites on the A, Assabet River; and B, tributaries, Assabet River

Basin 53

29 Observed and model-calculated monthly nonstorm streamflow for the calibrated transient model and for several alternative model parameters at the Assabet River

at Maynard and a selected tributary site in the Assabet River Basin Horizontal and vertical hydraulic conductivity of stratified glacial deposits multiplied and divided

by 2 for the A, Assabet River at Maynard and B, Cold Harbor Brook; horizontal and vertical hydraulic conductivity of till multiplied and divided by 2 for the C, Assabet River at Maynard and D, Cold Harbor Brook; storage property of stratified glacial deposits increased and decreased by 50 percent for the E, Assabet River at Maynard and F, Cold Harbor Brook; recharge fluctuations during the annual cycle

and evapotranspiration rate in wetlands and nonwetland areas decreased by

50 percent for the G, Assabet River at Maynard and H, Cold Harbor Brook 56

30 Model-calculated average A, March; and B, September inflows to and outflows

from the surficial layer of the simulated ground-water-flow system in subbasins

of the Assabet River Main Stem and tributary subbasins, 1997–2001, Assabet River Basin 60

31 Model-calculated components of average A, March; and B, September nonstorm

streamflow in subbasins of the Assabet River Main Stem 61

32 Model-calculated average A, March and B, September total nonstorm streamflow

and the component of streamflow that originated as wastewater, for existing conditions and two hypothetical scenarios of altered withdrawals and discharges

in the Assabet River Basin 62

33 Model-calculated average A, annual; B, March; and C, September nonstorm

streamflow from subbasins of the Assabet River Main Stem and tributaries for comparison with minimum streamflow requirements for the protection of aquatic habitat 63

34 Model-calculated changes, relative to simulated 1997–2001 conditions, in average annual inflows to and outflows from the surficial layer of the simulated ground-

water-flow system in subbasins of the A, Assabet River Main Stem; and B, tributary

subbasins, in a hypothetical scenario of no anthropogenic water management in the Assabet River Basin 68

35 Map showing changes in sewer lines and areas of septic-system return flow simulated in a hypothetical scenario of increased withdrawals and discharges

in the Assabet River Basin 70

36, 37 Graphs showing:

36 Model-calculated changes, relative to simulated 1997–2001 conditions, in average annual inflows to and outflows from the surficial layer of the simulated

ground-water-flow system in subbasins of the A, Assabet River Main Stem; and

B, tributary subbasins, in a hypothetical scenario of increased withdrawals

and discharges in the Assabet River Basin 71

37 Model-calculated components of average A, March; and B, September

nonstorm streamflow in subbasins of the Assabet River Main Stem, in a hypothetical scenario of increased withdrawals and discharges in the Assabet River Basin 72

38 Map showing hypothetical ground-water discharge sites for wastewater used in

simulations in the Assabet River Basin: A, Fort Meadow Brook subbasin in Hudson;

B, Taylor Brook subbasin in Maynard; C, Cold Harbor and Howard Brooks subbasin

in Northborough; and D, Stirrup Brook subbasin in Westborough 73

39, 40 Graphs showing:

39 Model-calculated average annual, March, and September nonstorm

streamflow in tributaries to the Assabet River for existing conditions and

scenarios of hypothetical ground-water discharge of wastewater at four

sites in the Assabet River Basin: A, Fort Meadow Brook ; B, Taylor Brook;

C, Cold Harbor Brook; and D, Stirrup Brook 76

40 Monthly withdrawal and discharge rates for 1997–2001 and for the

management-model applications for decreased streamflow depletion in the

Assabet River and tributaries in low-flow months in the upper part of the

Assabet River Basin: A OPT1; B, OPT2; C, OPT3; D, OPT4; E, OPT5; F, OPT6;

and G, 1997–2001 84

Tables

1 Hydraulic properties of stratified glacial deposits as determined by analysis of

aquifer tests at public-supply wells in the Assabet River Basin, eastern

Massachusetts .8

2 Average annual recharge rates and precipitation for the Assabet River Basin 11

3 Characteristics and water levels at observation wells and ponds in the Assabet

River Basin .14

4 Characteristics and water levels at long-term observation wells near the Assabet

River Basin .15

5 Drainage-area characteristics and mean annual flows at streamflow-gaging stations

in and near the Assabet River Basin .18

6 Drainage-area characteristics and mean annual flows at streamflow-measurement

sites in the Assabet River Basin .19

7 Population on public water and sewer and per capita water use in the Assabet

River Basin, 2000 25

8 Permitted water-supply withdrawals and wastewater discharges in the Assabet

River Basin .27

9 Existing (1997-2001) and permitted withdrawals for municipal public-water systems

in the Assabet, Sudbury, and Concord River Basins .30

10 Simulated water withdrawals and discharges in calibrated models (1997–2001) and

in scenario 2 for permitted withdrawals and wastewater discharges and unpermitted

golf-course withdrawals in the Assabet River Basin 38

11 Steady-state model-calculated average annual water levels and observed water

levels at observation wells and ponds in the Assabet River Basin .41

12 Steady-state model-calculated average annual nonstorm streamflow and observed

nonstorm streamflow at measurement sites in the Assabet River Basin 42

13 Steady-state model-calculated average annual water budget for the Assabet

River Basin .45

14 Water-level-fluctuation residuals and mean absolute-flow residuals for the calibrated

transient model and model runs that use alternative model parameters, Assabet River

Basin 57

15 Transient model-calculated average March and September water budgets for the

Assabet River Basin 59

16 Model-calculated mean monthly nonstorm streamflows for August and September

at sites for comparison with minimum streamflow requirements for habitat protection,

Assabet River Basin 64

17 Model-calculated nonstorm streamflow from subbasins in the Assabet River Basin for existing conditions (1997-2001) and two scenarios of altered water-management practices 67

18 Hypothetical ground-water discharge sites for wastewater used in simulations in the Assabet River Basin 75

19 Hydrologic response coefficients for the public-supply wells and a hypothetical ground-water-discharge site in the upper Assabet River Basin 80

20 Model-calculated average monthly nonstorm streamflow, 1997-2001, and changes

in monthly average nonstorm streamflow determined by solutions to management models in the upper Assabet River Basin 83

Conversion Factors, Datums, and Abbreviations

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)cubic foot per second per square mile (ft3/s/mi2) 0.01093 cubic meter per second per square kilometer

(m3/s/km2)

gallon per person per day (gal/person/d) 0.00378 cubic meter per person per day(m3/person/d)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)square foot per day (ft2/d) 0.0929 square meter per day (m2/d)

Temperature in degrees Fahrenheit (°F) can be converted to degrees Celsius (°C) as follows:

°C = (°F - 32) x 0.5555

In this report, vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29), and horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83) Altitude above the vertical datum is referred to as elevation.ABF Aquatic Base Flow

GIS Geographic Information System MADCR Massachusetts Department of Conservation and Recreation MADEP Massachusetts Department of Environmental Protection MWRA Massachusetts Water Resources Authority

NPDES National Pollution Discharge Elimination System TMDL Total Maximum Daily Load

USGS U.S Geological Survey

Simulation of Ground-Water Flow and Evaluation of

Water-Management Alternatives in the Assabet

River Basin, Eastern Massachusetts

By Leslie A DeSimone

Abstract

Water-supply withdrawals and wastewater disposal in the

Assabet River Basin in eastern Massachusetts alter the flow and

water quality in the basin Wastewater discharges and

stream-flow depletion from ground-water withdrawals adversely affect

water quality in the Assabet River, especially during low-flow

months (late summer) and in headwater areas Streamflow

depletion also contributes to loss of aquatic habitat in tributaries

to the river In 1997–2001, water-supply withdrawals averaged

9.9 million gallons per day (Mgal/d) Wastewater discharges

to the Assabet River averaged 11 Mgal/d and included about

5.4 Mgal/d that originated from sources outside of the basin

The effects of current (2004) and future withdrawals and

discharges on water resources in the basin were investigated in

this study

Steady-state and transient ground-water-flow models were

developed, by using MODFLOW-2000, to simulate flow in the

surficial glacial deposits and underlying crystalline bedrock in

the basin The transient model simulated the average annual

cycle at dynamic equilibrium in monthly intervals The models

were calibrated to 1997–2001 conditions of water withdrawals,

wastewater discharges, water levels, and nonstorm streamflow

(base flow plus wastewater discharges) Total flow through the

simulated hydrologic system averaged 195 Mgal/d annually

Recharge from precipitation and ground-water discharge to

streams were the dominant inflow and outflow, respectively

Evapotranspiration of ground water from wetlands and

non-wetland areas also were important losses from the hydrologic

system Water-supply withdrawals and infiltration to sewers

averaged 5 and 1.3 percent, respectively, of total annual

out-flows and were larger components (12 percent in September) of

the hydrologic system during low-flow months Water budgets

for individual tributary and main stem subbasins identified

areas, such as the Fort Meadow Brook and the Assabet Main

Stem Upper subbasins, where flows resulting from

anthropo-genic activities were relatively large percentages, compared to

other subbasins, (more than 20 percent in September) of total

out-flows Wastewater flows in the Assabet River accounted for

55, 32, and 20 percent of total nonstorm streamflow (base flow

plus wastewater discharge) out of the Assabet Main Stem Upper, Middle, and Lower subbasins, respectively, in an average September

The ground-water-flow models were used to evaluate water-management alternatives by simulating hypothetical scenarios of altered withdrawals and discharges A scenario that included no water management quantified nonstorm stream-flows that would result without withdrawals, discharges, septic-system return flow, or consumptive use Tributary flows in this scenario increased in most subbasins by 2 to 44 percent relative

to 1997–2001 conditions The increases resulted mostly from variable combinations of decreased withdrawals and decreased infiltration to sewers Average annual nonstorm streamflow in the Assabet River decreased slightly in this scenario, by 2 to 3 percent annually, because gains in ground-water discharge were offset by the elimination of wastewater discharges

A second scenario quantified the effects of increasing withdrawals and discharges to currently permitted levels In this simulation, average annual tributary flows decreased in most subbasins, by less than 1 to 10 percent relative to 1997–2001 conditions In the Assabet River, flows increased slightly, 1 to

5 percent annually, and the percentage of wastewater in the river increased to 69, 42, and 27 percent of total nonstorm streamflow out of the Assabet Main Stem Upper, Middle, and Lower subbasins, respectively, in an average September

A third set of scenarios quantified the effects of water discharge of wastewater at four hypothetical sites, while maintaining 1997–2000 wastewater discharges to the Assabet River Wastewater, discharged at a constant rate that varied among sites from 0.3 to 1.5 Mgal/d, increased nonstorm streamflow in the tributaries adjacent to the sites and in down-stream reaches of the Assabet River During low-flow months, flow increases in tributaries were less than the constant dis-charge rate because of storage effects and increased ground-water evapotranspiration Average September flows, however, more than doubled in these scenarios relative to simulated 1997–2001 conditions in Fort Meadow, Taylor, Cold Harbor, and Stirrup Brooks Increases in Assabet River flows were small, with reductions in the wastewater component of flow in September of 5 percent or less

ground-Simulation-optimization analysis was applied to the upper

part of the basin to determine whether streamflow depletion

could be reduced, relative to 1997–2001 conditions, by

management of monthly withdrawals, with and without

ground-water discharge The analysis included existing supply wells,

one new well (in use since 2001), and a hypothetical discharge

site in the town of Westborough Without ground-water

discharge, simulated nonstorm streamflow in September in the

Assabet River about doubled at the outlet of the Main Stem

Headwaters subbasin and increased by about 4 percent at the

outlet of the Main Stem Upper subbasin These increases were

obtained by using water-supply sources upstream of lakes,

which appeared to buffer the temporal effect of withdrawals, in

low-flow months, and by using water-supply sources adjacent

to streams, which immediately affected flows, in high-flow

months With ground-water discharge, simulated flows nearly

tripled at the outlet of the Assabet Main Stem Headwaters

subbasin, increased by 18 percent at the outlet of the main stem

Upper subbasin, and more than doubled in a tributary stream

The general principles illustrated in the simulation-optimization

analysis could be applied in other areas of the basin where

streamflow depletion is of concern

Introduction

Water-supply withdrawals and wastewater disposal in

the Assabet River Basin, an area of about 177 mi2 in eastern

Massachusetts (fig 1), have altered the flow and quality of

ground- and surface water in the basin Ground water is

with-drawn for municipal supply from the discontinuous glacial

aquifers along the tributaries and main stem of the Assabet

River Because these aquifers are in direct hydraulic connection

with surface waters, the withdrawals typically reduce

ground-water discharge to streams and wetlands and deplete

stream-flow (Winter and others, 1998; Randall, 2001) Along with

water imported from outside the basin, private wells, and a few

water-supply reservoirs, these ground-water sources supply a

growing population of about 130,000 in the basin Publicly

supplied water typically is transferred within or outside of the

basin after use to downstream treatment facilities, where it is

discharged to the main stem of the Assabet River These water

withdrawals, transfers, and discharges adversely affect water

resources by reducing flows required to maintain aquatic

habitat, degrading water quality, and altering wetlands

Currently (2004), the Assabet River is eutrophic during

the summer and fails to meet most applicable water-quality

standards (Massachusetts Department of Environmental

Protection, 2003) These conditions result from discharges from

the four municipal wastewater-treatment facilities along the

river, from nonpoint sources, and from past waste-disposal

practices (Richardson, 1964; ENSR International, 2001; Earth

Tech, 2002a; Organization for the Assabet River, 2003b)

Ground-water withdrawals also affect water quality and

quantity Natural ground-water discharge to streams, either to

tributaries or directly to the main stem river, provides

high-quality base flow that dilutes wastewater discharges Reduced ground-water discharge to streams resulting from withdrawals for water supply may exacerbate the poor water-quality conditions common during low-flow periods Reductions

in current waste loads to the river are planned, primarily through the TMDL (Total Maximum Daily Load) process (Massachusetts Department of Environmental Protection, 2003) Actions to achieve waste-load reductions are costly, however, and alternative approaches to improving water quality

in the river that involve ground-water management also are being considered (Earth Tech, 2002a)

Demands on water resources in the Assabet River Basin for water supply and wastewater disposal are likely to increase The basin is along the rapidly developing Interstate

495 corridor, where a growing technology industry has spurred residential, commercial, and industrial development (Massachusetts Technology Collaborative, 1998) Between

1985 and 1999, 7.5 percent of the total basin area was converted from forested or agricultural uses to developed uses, with areas

of residential and commercial or industrial land use increasing

by 27 and 22 percent, respectively (MassGIS, 2001) Average population growth between 1990 and 2000 in towns in the basin, at 15 percent, was nearly 3 times the statewide average, and exceeded 30 percent in some towns (U.S Census Bureau, 2003) These trends are likely to continue, resulting in the need for additional water supplies and wastewater discharges beyond current conditions (Massachusetts Technology Collaborative, 1999)

A better understanding of the effects of current and future water withdrawals and discharges on streamflows in the Assabet River and its tributaries will help water-resource managers make decisions about water supply, wastewater disposal, and waste-load reduction Evaluating the effects of water-management practices on streamflows in a regional context also will aid management decisions, because these effects accumulate downstream Recognition of this need

by State agencies and others prompted a study by the U.S Geological Survey (USGS), in cooperation with the Massachusetts Department of Conservation and Recreation (MADCR) The objective was to evaluate the effects on streamflows in the basin of withdrawals, discharges, and water-management alternatives, such as ground-water disposal of wastewater Ground-water-flow models were developed to meet this objective because of the important role of ground-water discharge to streams and because most water withdrawals

in the basin are from ground water To ensure that the gation adequately addressed issues of concern in the basin, representatives from Federal and State agencies, towns, a watershed association, and other organizations participated

investi-in a Technical Advisory Committee (TAC) for the study The water-use and management issues of concern in the Assabet River Basin are common to many other basins in eastern Massachusetts and adjacent States, where communities are striving to balance growth and the available water resources The methods and results of this study provide tools that can be used to address these issues

ASSABET MAIN STEM MIDDLE SUBBASIN

DANFORTH BROOK SUBBASIN

ELIZABETH BROOK SUBBASIN

FORT POND BROOK SUBBASIN

TAYLOR BROOK SUBBASIN

SPENCER BROOK SUBBASIN

NASHOBA BROOK SUBBASIN

ASSABET MAIN STEM LOWER SUBBASIN

ASSABET MAIN STEM UPPER SUBBASIN

STIRRUP BROOK SUBBASIN

EXPLANATION

0 1 2 3 4 5 KILOMETERS From USGS and MassGIS data sources, Massachusetts State Plane

Coordinate System, Mainland Zone

01097000 ACW158

POND WETLAND BASIN AND SUBBASIN BOUNDARY TOWN BOUNDARY

STREAM-GAGING STATION AND NUMBER

LONG-TERM OBSERVATION WELL AND IDENTIFIER

Lake Boon

White Pond

Warner Pond

Nagog Pond

Little Chauncy Lake Bartlett Pond

Lake Williams

Fort Meadow Resevoir

Millham Resevoir Rocky

Pond

Delaney Pond

Long Pond Fort Pond

Gates Pond

H ow ar

d B ro ok

North Brook N ort h B roo k

Stirrup Brook Stir ru

p B roo k

Fort P ond Brook Fort Pon d Brook

Sp en

ce r

Dan for th

B ro

ok

A ssa bet R iver

A1 Impoundment Chauncy Lake

Lake Boon

White Pond

Warner Pond

Nagog Pond

Little Chauncy Lake Bartlett Pond

Lake Williams

Fort Meadow Reservoir

Millham Reservoir Rocky

Pond

Delaney Pond

Long Pond Fort Pond

Gates Pond

Hop Brook

Cold Harbor

Brook

Ho w ard Brook North Brook

Stirrup Brook

Fort P ond Brook

Sp en

ce r

Dan for th

B ro

E liz ab

42o30'

73o00' 72 o

00'

71 o 00'

70 o 00'

41 o 30'

STUDY BASIN

0 10 20 30 40 50 KILOMETERS

0 10 20 30 40 50 MILES

BASIN BOUNDARIES

MASSA CH USETTS BA Y

A

TL AN

Purpose and Scope

This report describes current water-resource conditions in

the Assabet River Basin, the development, calibration, and

limitations of numerical ground-water-flow models for the

basin, and simulations made with the models to evaluate the

effects of water withdrawals and discharges on streamflows It

also presents the data collected to define water resources in the

basin, and upon which the steady-state and transient models

were developed The models include average water

with-drawals and discharges for a 5-year period, 1997–2001, which

was near long-term average hydrologic conditions Simulation

results of several scenarios of altered withdrawals, discharges,

or other water-management practices also are described

Finally, the report describes the use of optimization techniques

to investigate the potential for reduced streamflow depletion

through altered water-management practices in the upper part

of the basin

Description of the Study Area

The Assabet River Basin (fig 1) encompasses an area

of 177 mi2 within the Merrimack River Basin in eastern

Massachusetts The study area includes all or part of 20 towns

The basin is elongate in the northeast-southwest direction,

parallel to regional geologic features (Zen and others, 1983)

Topography varies from gently rolling to hilly, with elevations

ranging from about 100 to 750 ft above NGVD 29 Higher

elevations and steeper slopes are along the northwestern

boundaries of the basin The Assabet River flows northeastward

from Westborough, through lowlands near the eastern basin

boundary, about 31 mi to its confluence with the Sudbury River

in Concord, MA The climate is humid and temperate

Precipi-tation averages 47 in/yr, and average temperature ranges from

25°F in January to 71°F in July, according to records from

nearby weather stations (National Oceanic and Atmospheric

Administration, 2002)

Land use in the Assabet River Basin in 1999 was primarily

forested or open (51 percent) and residential (28 percent, mostly

low and medium density), with agricultural (8 percent),

commercial or industrial (5 percent), water and wetlands (5

percent) representing small fractions of the basin area

(MassGIS, 2001) Land use and population density varied

widely among towns Population density ranged from about 200

to nearly 2,000 people/mi2 in 2000 (U.S Census Bureau, 2003)

Towns varied in residential land use from 13 to 39 percent, and

in commercial or industrial land use and in agricultural land use

from less than 1 to 14 percent each (1999 data; MassGIS, 2001)

Forest cover varied from 34 to 66 percent, in 1999 Densely

developed areas clustered along the main stem Assabet River

and near the southeastern boundary of the basin The most

rapidly growing towns, however, were in the headwaters and

along the northwestern upland parts of the basin; these include Bolton, Boxborough, Shrewsbury, Westborough, and Westford (fig 1) Population increased in these towns from 27 to 46 percent between 1990 and 2000 (U.S Census Bureau, 2003)

Previous Studies

Information on the hydrogeology and water resources

of the Assabet River Basin is available from many sources Several publications describe the surficial geology of parts of the study area (Campbell, 1925; Jahns, 1953; Hansen, 1956; Perlmutter, 1962; Koteff, 1966; and Shaw, 1969) Basic hydro-geologic data, including well and boring logs, water levels, and the locations of high transmissivity zones, are described in Pollock and Fleck (1964), Pollock and others (1969), and Brackley and Hansen (1985) An analysis of aquifer yields developed on the basis of streamflow data was completed by Bratton and Parker (1995) Continuous-record streamflow data for the Assabet River and for Nashoba Brook, a tributary of the Assabet River, are available from two long-term USGS streamflow-gaging stations (fig 1; Socolow and others, 2003) Historical streamflow data also were collected at partial-record stations in the basin that were used for USGS low-flow studies (Ries, 1993, 1994, and 1999; Ries and Friesz, 2000) Stream-flow and other hydrologic data for the Assabet River and its tributaries were collected for a recently completed TMDL study, in support of a surface-water model of the basin (ENSR International, 2001, 2004) Data also were being collected at the time of this study by the Organization for the Assabet River (2003a), as part of a stream monitoring and public-outreach program Streamflow requirements for the protection of aquatic habitat were recently assessed by Parker and others (2004) at six sites in the basin A water-use investigation of the Assabet, Concord, and Sudbury River Basins (L.K Barlow, U.S Geological Survey, oral commun., 2003) was ongoing at the time of this study Information on existing conditions of water use and disposal for communities in the Assabet Consortium were available in the Comprehensive Wastewater Management Plans for these towns (Camp, Dresser, & McKee, 2001; 2002; Dufresne-Henry, 2001, 2002; Earth Tech 2001a, 2001b, 2001c, 2001d, 2001e, 2002b, 2002c, 2002d; Fay, Spofford, and Thorndike, 2001a, 2001b, 2002a, 2002b) The Assabet River Consortium includes the six towns (Hudson, Marlborough, Maynard, Northborough, Shrewsbury, and Westborough) in the basin that discharge wastewater to the river (Earth Tech, 2001a) Also, consultants to the towns have completed many small-scale hydrogeologic investigations These studies were completed to locate water-supply sources, to determine well-head protection areas for public-supply wells, to investigate ground-water contamination, or to support specific develop-ment projects Information available from these reports include well and boring logs, hydrogeologic maps and sections, and

results of aquifer tests and numerical simulations Consultant

reports used in this study include ABB Environmental Services

(1996), Camp, Dresser, & McKee (1990), Dufresne-Henry

(1981, 1989, 1993, 1996, 1999), Earth Tech (2000a, 2000b,

2000c, 2000d, 2000e), Ecology and Environment (1994),

Epsilon Associates (2000, 2002a, 2002b), Geologic Services

Corporation (1984, 1985, 1987, 1989, 1995a, 1995b, 1996,

2000), GeoScience Consultants (1988), GeoTrans (2001),

Goldberg-Zoino & Associates (1985), Goldberg, Zoino,

Dunnicliff & Associates (1980a, 1980b), HMM Associates

(1987), Keystone Environmental Resources (1991), McCulley,

Frick, & Gilman (1997), Metcalf & Eddy (1994), Rizzo

Associates (1990), Sasaki Associates (1989), Weston &

Sampson Engineers (1997), and Whitman & Howard (1986,

1987a, 1987b, 1987c)

Ground- and Surface-Water

Resources

Many factors affect water resources in the Assabet River

Basin Ground-water flow is influenced by the hydraulic

properties of the geologic units in which it occurs and the timing

and quantity of recharge Impoundments, ponds, and wetlands,

as well as climate and topography, affect surface-water flow

Ground-water- and surface-water-flow systems are in close

hydraulic connection, especially in the surficial geologic

materials

Geologic Setting

Ground water occurs in three major geologic units in the

Assabet River Basin—stratified glacial deposits, glacial till, and

bedrock (fig 2) The stratified glacial deposits consist of sorted

and layered sand, gravel, silt, and clay deposited by meltwater

in streams or lakes in valleys and lowlands during the last

glacial period The till is generally an unsorted, unstratified

mixture of clay, silt, sand, gravel, cobbles, and boulders,

deposited directly by the glacial ice Locally, till forms thick

deposits in uplands or in areas of stratified glacial deposits and

covers uplands in a thin layer Crystalline bedrock underlies the

stratified glacial deposits and till, and consists primarily of

metasedimentary, metavolcanic, and metaintrusive rocks (Zen

and others, 1983) Alluvium and swamp deposits are relatively

minor components of the hydrogeologic system in the basin,

and are not areally extensive and (or) form relatively thin

surficial layers

Although the stratified glacial deposits are discontinuous

and heterogeneous, they are the most productive aquifers in

the basin They occur along the Assabet River and its major

tributaries and cover about 43 percent of the study area (fig 2) The areal extent of stratified glacial deposits in the basin was determined from published and unpublished surficial geologic maps (J.R Stone, U.S Geological Survey, written commun., 2002) The thickness of the stratified glacial deposits was mapped by contouring the elevation of the underlying bedrock

or till surface (J.R Stone, U.S Geological Survey, written commun., 2002) and subtracting that elevation from the land-surface elevation Data on depth to bedrock, till, or drilling refusal were obtained from about 830 well logs or borings, available from USGS files, from the reports by private consultants cited previously, and from wells installed during this study The thickness of the stratified glacial deposits ranges from 0 at its edges to about 160 ft (fig 2) Typically, the deposits are less than 75 ft thick, and average only about 35 ft thick throughout the mapped area Stratified glacial deposits are relatively thick in southeastern Stow, where a bedrock valley may represent the preglacial route of the Assabet River (Hansen, 1956; Perlmutter, 1962), and in Concord and southeastern Acton (fig 2)

The stratified glacial deposits in the Assabet River Basin were deposited during successive pauses of the retreating ice margin in association with two meltwater lakes, glacial Lakes Assabet and Sudbury (Campbell, 1925; Hansen, 1956; Koteff, 1966; J.R Stone, U.S Geological Survey, oral commun., 2002) They include glacial stream, deltaic, and lake-bottom deposits Distinct sequences of these units, as have been identified elsewhere in New England (Stone and others, 1998; Randall, 2001), have not been identified in the Assabet River Basin, and geologic mapping has not distinguished sediment packages based on lithology or depositional setting Ice-contact deposits, variable in thickness, grain size, and sorting, are common throughout the basin These stratified glacial deposits are characteristic of the low-relief, narrow valleys in southern New England (Randall, 2001) The areas of thick stratified glacial deposits in southeastern Stow and Concord, mapped as outwash plain and delta deposits, include sediments that were deposited farther from the ice margin and are better sorted than the more proximal ice-contact deposits (Hansen, 1956; Koteff, 1963) Also, near the Assabet River from Stow to Concord, thick layers of fine sand, silt, and clay underlie coarser-grained sediments Fine-grained sediments also occur at depth farther south in Northborough and Westborough; fine-over-coarse sequences also are common in Westborough These fine-grained sediments probably are lake-bottom sediments (Koteff, 1963); their distribution, however, is discontinuous In areas of coarse-grained deposits, depressions left by melting ice blocks are common and often are occupied by kettle lakes or isolated wetlands

STRATIFIED GLACIAL DEPOSITS THICKNESS, IN FEET

THIN TILL AND BEDROCK THICK TILL

BASIN BOUNDARY TOWN BOUNDARY

0 1 2 3 4 5 KILOMETERS From USGS and MassGIS data sources, Massachusetts State Plane

Coordinate System, Mainland Zone

71 o 36'

71 o 24'

Till in the Assabet River Basin consists of a thin upper till

and a discontinuous, thick lower till The upper or younger till

forms a thin surficial layer over bedrock throughout the basin

The till is loosely consolidated, relatively permeable,

character-ized by abundant boulders, and typically 10 to 15 ft thick or less

(Campbell, 1925; Jahns, 1953; Hansen, 1956; Koteff, 1966)

The lower or older till forms hills with deposits that often are 50

to 80 ft thick, and may exceed 100 or 200 ft thick The thick

lower till is compacted tightly and relatively impermeable Hills

of thick till (drumlins) are rounded and commonly elongate in

the north-south direction, parallel to the direction of regional ice

flow Because of its low transmissivity, till rarely is used for

water supply in the basin, even by domestic water users

Bedrock consists of Proterozoic or Lower Paleozoic

metasedimentary, metavolcanic, and intrusive igneous rocks,

including the Nashoba Formation, Andover Granite, and

Marlboro Formation (Zen and others, 1983; Goldsmith, 1991a)

Typical rock types are mica schist and gneiss, granite, diorite,

and amphibolite The basin lies in a structural zone between two

major fault zones, which trend northeast-southwest across

the State Within this zone, beds dip steeply and faulting is

pervasive and complex (Goldsmith, 1991b; Walsh, 2001) Two

regional faults within the basin, the Assabet River and Spencer

Brook faults, extend northeast-southwest from Northborough to

West Concord Faults and joints are important hydrologically,

because most water in bedrock is stored and flows in these

openings; the unbroken rock is nearly impermeable

Hydraulic Properties

Information about the hydraulic properties of

hydrogeo-logic units in the basin is most readily available for the stratified

glacial deposits than for the other geologic units, because large

water supplies commonly are developed in these deposits

Horizontal hydraulic conductivity values at public-supply

wells, determined from analysis of aquifer tests, averaged about

190 ft/d (median value equal to 140 ft/d) and ranged from 80

to 675 ft/d (table 1) These values likely represent the most

permeable and most productive deposits in the basin Well logs,

distributed throughout the stratified glacial deposits, are another

source of information about hydraulic properties of sediments

Brackley and Hansen (1985) used horizontal hydraulic

conduc-tivity values estimated from well logs, along with other data,

to map transmissivity (hydraulic conductivity multiplied by

aquifer thickness) in the basin The estimates were based on

values for sediments of various grain size and sorting in New

England, compiled from aquifer tests and other sources (B.P

Hansen, U.S Geological Survey, oral commun., 2002) The

values determined by Brackley and Hansen (1985), and similar values calculated for well logs inventoried in this study, were used to characterize horizontal hydraulic conductivity in the stratified glacial deposits (fig 3) Spatially, hydraulic conduc-tivity values from well logs and aquifer tests are variable, which reflects the vertical and horizontal heterogeneity of sediment characteristics (for well logs) because the values are depth-weighted averages Hydraulic conductivity values, however, were significantly different among the mapped transmissivity zones, with geometric mean values of 46, 72, and 108 ft/d for low-, medium-, and high-transmissivity zones, respectively Little information about vertical hydraulic conductivity is available for stratified glacial deposits in the study area, but values can be estimated from reported ratios of vertical to horizontal conductivity Reported ratios range from 1:3 to 1:5, for coarse-grained stratified glacial deposits, and from 1:30 to 1:100, for fine-grained deposits (Dickerman and others, 1990; Masterson and Barlow, 1997; Masterson and others, 1998; Stone and Dickerman, 2002) Reported values of specific yield,

or unconfined storage coefficient, of stratified glacial deposits ranges from 0.16 to 0.47, with typical values of 0.25 to 0.33 for medium to coarse sand and gravel, 0.21 to 0.33 for fine sand, and 0.02 to 0.08 for silt and clay (Johnson, 1967; Morris and Johnson, 1967; Moench and others, 2000; Kontis and others, in press) Storage coefficients from aquifer tests in coarse-grained deposits in the basin range from 0.07 to 0.14 (table 1); these values may be representative of short-term aquifer responses to stress Less information is available for confined storage coeffi-cient for stratified glacial deposits than for specific yield Typical values of specific storage are 1×10-4 ft-1 for fine-grained deposits and 1×10-6 ft-1 for coarse-grained deposits in the glaciated northeastern United States (Kontis and others, in press); these values would need to be multiplied by aquifer thickness to determine the storage coefficient

Hydraulic properties of till are not well known Horizontal hydraulic conductivity of till in the study area probably ranges from 0.01 to 10 ft/d (Allen and others, 1963; Randall and others, 1988; Melvin and others, 1992; Tiedeman and others, 1997; Lyford and others, 2003; Kontis and others, in press), with the thin till at the upper end of the reported range The ratio of vertical to horizontal hydraulic conductivity may range from 1:1 to 1:100 The vertical hydraulic conductivity of thin surficial deposits, consisting of lake-bottom silt, fine sand, and thin till, as determined from an aquifer test for municipal supply wells in Maynard, ranges from 0.13 to 1.35 ft/d, averaging 0.48 ft/d (Lyford and others, 2003) Specific yield values of 0.06 to 0.26 have been reported for silty and sandy till (Allen and others, 1963; Morris and Johnson, 1967)

1Bay State Circuits,

nduc- tiv ity (ft/ d)

Storage coeffi- cient

0 1 2 3 4 5 KILOMETERS From USGS and MassGIS data sources, Massachusetts State Plane

Coordinate System, Mainland Zone

TRANSMISSIVITY OF STRATIFIED GLACIAL DEPOSITS, IN FEET SQUARED PER DAY Less than 1,350 1,350–4,000 Greater than 4,000 TILL AND BEDROCK BASIN BOUNDARY TOWN BOUNDARY

HYDRAULIC CONDUCTIVITY— Water-supply wells shown in blue Symbol size is proportional to value,

in feet per day 10

50 150 250

Figure 3 Depth-weighted hydraulic conductivity from well logs and transmissivity zones in stratified glacial deposits in the

Assabet River Basin, eastern Massachusetts Transmissivity zones from Brackley and Hansen (1985)

Hydraulic properties of bedrock generally are low but

variable Median values of hydraulic conductivity of crystalline

bedrock for large and small supply wells in New England and

adjacent areas range from 0.45 to 0.9 ft/d (Randall and others,

1966; Randall and others, 1988) Hydraulic conductivity in

fractured crystalline bedrock in the Mirror Lake area, New

Hampshire, varies over 6 orders of magnitude; representative

values determined through model calibration were 0.02 and

0.09 ft/d (Tiedeman and others, 1997) Aquifer tests of four

industrial supply wells in Acton and Hudson yielded hydraulic

conductivity values of 0.18, 0.24, 0.97, and 2.8 ft/d (Epsilon

Associates, 2000, 2002a, 2002b) The values for supply wells in

bedrock, in the study area and elsewhere, likely represent the

more permeable bedrock zones Little information is available

on vertical conductivity or storage properties of bedrock, which

are likely to be highly variable Vertical conductivity at the

Maynard supply-well site ranged from 0.13 to 1.35 ft/d (Lyford

and others, 2003) Storage coefficients for the industrial supply

wells in Hudson and Acton ranged from 3×10-6 to 0.067

(Epsilon Associates, 2000, 2002a, 2002b), and a median value

for large supply wells in New England was about 2×10-4

(Randall and others, 1988)

Ground-Water Flow

Ground water in the study area generally flows from

topographic highs in the uplands toward stream channels and

toward the stratified glacial deposits in valleys and lowlands

The water table mimics topography, such that surface- and

ground-water divides typically coincide, especially in uplands

Precipitation recharges ground water in till and bedrock upland

areas and in the stratified glacial deposits; surface runoff from

uplands also recharges the stratified glacial deposits at the edges

of valleys Ground-water levels and flow directions,

particu-larly in the stratified glacial deposits, are strongly influenced by

the locations and elevations of streams, which, along with

wetlands and pumping wells, are the discharge points for the

ground-water-flow system (Winter and others, 1998; Randall

and others, 2001)

Recharge

Recharge rates for the Assabet River Basin were estimated

from two approaches and data sources—streamflow records

and climate data The recharge estimates were made to

charac-terize the overall water budget for the basin and to guide

calibration of the ground-water-flow models The

recession-curve displacement method was applied to mean daily

stream-flow records from the two continuous-record streamstream-flow-

streamflow-gaging stations (fig 1) in the basin The computer program

RORA, developed by Rutledge (1993, 1998) on theory by Rorabaugh (1964), was used to estimate recharge rates In this method, recharge is quantified from the upward displacement of the streamflow-recession hydrograph after streamflow peaks Individual recharge events are summed over yearly and monthly intervals Several simplifying assumptions about the flow system are made, including the assumption of uniform aquifer properties and an instantaneous and uniform aquifer response to recharge events throughout the basin

A water-balance method also was used to calculate daily recharge from climate data as:

where

Climate data from the nearby Bedford and West Medway, MA, weather stations (about 5 and 15 mi, respectively, from the basin) were used for this analysis because they were considered most representative of conditions in the study area Potential evapotranspiration (PET) for use in the water-balance method was calculated by using methods for estimating evaporation in settings where actual evaporation equals PET The Hamon (1961) method (Lumb and Kittle, 1995) and the available climate data (mean daily temperature and hours of sunlight) initially were used Because the Hamon method underestimates actual evaporation (Winter and others, 1995), values from this method were adjusted upward based on a comparison of monthly PET values calculated by Hamon and Penman methods for a basin in southern Rhode Island (P.J Zarriello, U.S Geological Survey, written commun., 2003) The Penman equation (Penman, 1948) more completely characterizes the driving forces of evaporation because it includes temperature, solar radiation, and wind speed; therefore, it is considered a better approximation of actual evaporation (Penman, 1948; Veihmeyer, 1964; Winter and others, 1995) The difference between mean daily streamflow and mean daily base flow (estimated with the automated hydrograph-separation method, PART; Rutledge, 1993, 1998) at the Assabet River streamflow-gaging station (fig 1) was used as an estimate of direct runoff Use of PART in an estimate of direct runoff assumes that anthropogenic effects on streamflow (for example, increased wastewater discharge to the river from storm inflow to sewers) are negligible compared to those resulting directly from precip-itation The water-balance method was applied by using a FORTRAN computer program (D.R LeBlanc, U.S Geological Survey, written commun., 2002) that calculates ET, soil

moisture deficit, and recharge on a daily basis, as described by

Thornthwaite and Mather (1957) ET is set equal to PET when

precipitation exceeds PET and is equal to precipitation and

available soil moisture when precipitation is less than PET The

remaining available water first goes to satisfy the soil moisture

deficit, then to recharge A maximum soil storage capacity of

2 in was assumed (Thornthwaite and Mather, 1957) No lag

time is applied between precipitation and recharge to the water

table, such that unsaturated-zone travel time is assumed

negligible As with the results produced by the RORA method,

the water-balance method results in basin-wide recharge rates

that simplify and homogenize recharge, runoff, and ET

processes

Recharge rates of about 20 in/yr were calculated from

streamflow records, for long-term conditions and for the 1997–

2001 period (table 2) The water-balance method yielded rates

of about 17 in/yr These values are consistent with recharge

rates of 17.5 to 25.5 in/yr, estimated from streamflow records

and model calibration for basins in southern New England with

variable percentages of stratified glacial deposits and

till-covered uplands (Bent, 1995, 1999; Barlow, 1997; Barlow and

Dickerman, 2001; DeSimone and others, 2002) Although

average annual rates for 1997–2001 are similar to long-term

rates, this 5-year period was unusual in that it contained

relatively dry summers in 1997 and 1999 and an extended

period of dry weather that began in September 2001 (fig 4)

Recharge rates of 17 to 20 in/yr for 1997–2001 correspond to

total inflow volumes to the basin of 143 to 169 Mgal/d (222 to

261 ft3/s)

1 Assabet River streamflow-gaging station, 1941–2002; Nashoba Brook

streamflow-gaging station, 1964–2002; water-balance method, 1958–2002.

The distribution of annual recharge among months from both methods (fig 5) is consistent with conceptual models in which most aquifer recharge occurs during spring and winter months Results of the two methods differ in that recharge rates from streamflow records have a distinct peak in the spring that may reflect the effects of snowmelt or aquifer storage that are not captured in the climate-based water-balance method Unlike the annual average rates, deviations of 1997–2001 conditions from long-term average conditions are apparent in the monthly average rates Average rates in October, November, and December for 1997–2001 are lower than long-term average rates for both methods because of the extended dry period in

2001 Average March and June rates for 1997–2001 are higher than the long-term average because of some unusually wet months in that 5-year period (figs 4 and 5) Both methods, however, are more accurate for estimating long-term average rates than for estimating rates at shorter time scales, such as months (Rutledge, 1998, 2000)

Water Levels

Ground-water levels throughout the basin are strongly influenced by the locations and elevations of streams, ponds, and wetlands Water-level fluctuations also are influenced by proximity to surface water Annual fluctuations are smallest near streams and ponds, and are largest in the uplands, where thin surficial layers of till may dry out in summer (Randall and others, 1988) In this study, ground-water levels were measured only in the stratified glacial deposits; water levels and fluctua-tions in the till and bedrock upland areas were considered too variable to be characterized by the data-collection program.Water levels were measured in 19 wells at about monthly intervals from September 2001 through December 2002 (fig 6 and table 3) Data also were available from a long-term observation well, ACW158, with a continuous record since July

2001 and a 40-year record of intermittent measurements (Socolow and others, 2003) The wells all were screened in the stratified glacial deposits Water levels throughout eastern Massachusetts during the measurement period were lower than normal, as shown by records at ACW158 (fig 7) and at other long-term observation wells (table 4; Socolow and others, 2002, 2003) Measured annual fluctuations in observation wells generally ranged from less than 2 to more than 4 ft Fluctuations generally were largest in wells near boundaries of stratified glacial deposits with uplands, such as ACW257 and WRW150, and smallest in wells near streams, such as HZW147 and WRW149 (fig 8)

Table 2 Average annual recharge rates and precipitation for the

Assabet River Basin, eastern Massachusetts

[in/yr, inches per year]

Period

itation (in/yr)

Precip-Recharge (in/yr) Streamflow hydrograph displacement method

balance method

Water-Assabet River station (01097000)

Nashoba Brook station (01097300)

Data source period

J F M A M J J A S O N D

MONTHLY MEAN, 1997-2002 LONG-TERM MONTHLY MEAN

Figure 4 Monthly mean precipitation for long-term average conditions (1958–2002) and for 1997–2002 at National

Oceanic and Atmospheric Administration weather stations in Bedford and West Medway, Massachusetts Data shown

are averages of daily values at the two stations

EXPLANATION

Figure 5 Monthly recharge rates estimated from A, streamflow records at the Assabet River streamflow-gaging

station in Maynard; B, streamflow records at the Nashoba Brook streamflow-gaging station; and C, climate data from

Bedford and West Medway weather stations, for long-term average conditions (period of record of data sources) and

1997–2001, Massachusetts

A9W53

WRW149 NUW128

WRW150

NUW130 NUW129

01096615 01096600

01096630 01096705

01096700

01096710

01096730 01096805

Wheeler Pond

A1 Impoundment

HZW147 HZW148 HZW149

01096840 01096838

01097380 01097412 01097300

ACW256 ACW257

ACW255

S3W184

Warner Pond

Delaney Pond

White Pond

Lake Boon

Assabet River at Hudson

Assabet River at Maynard West Pond

WWW160 WWW158

Coordinate System, Mainland Zone

01096840

Wheeler Pond A9W53

TILL OR BEDROCK STRATIFIED GLACIAL DEPOSITS

BASIN BOUNDARY STREAMFLOW- MEASUREMENT SITE OR GAGING STATION AND IDENTIFIER

OBSERVATION WELL AND IDENTIFIER

MEASUREMENT SITE FOR POND OR IMPOUNDMENT AND IDENTIFIER

71 o 36'

71 o 24'

42 o 18'

42 o 24'

42 o 30'

Figure 6 Streamflow-measurement sites, observation wells, and pond-measurement sites in the Assabet River Basin,

eastern Massachusetts

1 Screened interval equal to 9.7 feet Mean depth to water and mean water-level elevation for water year 2002 are averages of interpolated daily values.

2 No data for June 2002.

3 No data for April 2002.

4 Missing data for winter 2002 because of ice.

Table 3 Characteristics and water levels at observation wells and ponds in the Assabet River Basin, eastern Massachusetts.

[Site locations shown in figure 6 Wells are screened at bottom, with screened interval equal to 5 feet, unless otherwise indicated Latitude and longitude: In

degrees, minutes, and seconds NGVD, National Geodetic Vertical Datum; not applicable or not known; +, plus or minus]

Mean depth

to water (feet below land surface)

Mean water-level elevation (feet above NGVD 29)

Water year

2000

Estimated, 1997–2001 Water

level

90-percent confidence limits

Average water levels for 1997–2001 at observation wells

in the basin were estimated by relating the measured monthly

values to water levels at nearby long-term observation wells

Water levels at study sites initially were compared using

scatterplots with same-day water levels at 17 long-term wells

(table 4; only wells used are listed) Same-day water levels at

long-term wells were interpolated between measured values, if

necessary, by using the EXPAND procedure of SAS (SAS

Institute, 1993) For each study site, one to six long-term wells

were identified that correlated closely (R2 values of linear

regressions greater than 0.8) with the site Relations between

water levels at each study site and each long-term well were

developed by using the Maintenance of Variance Extension,

Type 1 (MOVE.1) method (Hirsch, 1982) The MOVE.1

equations were used to generate multiple estimates of mean

annual and monthly water level during 1997–2001 for each

study site, as described in DeSimone and others (2002); the

associated mean square error of each relation (MSE) was used

to combine the multiple estimates from each site into weighted

average estimates of mean annual and monthly water level for

1997–2001 (table 3) The MSE also was used to calculate

90-percent confidence intervals for the estimates, as described in

DeSimone and others (2002) Estimated annual average water

levels for 1997–2001 at observation wells were about from 0.5

to 1.5 ft higher than the measured values for water year 2000

(table 3) Estimated average monthly water levels for 1997–

2001 peaked earlier and higher than measured water levels,

which is consistent with the trends shown at the long-term

continuous-record monitoring well ACW 158 (fig 7)

J A O N D

LONG-TERM MONTHLY AVERAGE

DAILY AVERAGE, JULY 2001–

DECEMBER 2002 MONTHLY AVERAGE, 1997–2001

EXPLANATION

A ABO

Figure 7 Monthly and daily average water levels

at long-term observation well ACW158, Assabet River Basin, eastern Massachusetts

1 Open-end well, cased to depth listed.

2 Well screened in glacial till.

Table 4 Characteristics and water levels at long-term observation wells near the Assabet River Basin, eastern Massachusetts.

[Town: See Socolow and others (2003) for additional location information Well-screen interval: Wells screened in stratified glacial deposits, unless otherwise

indicated NGVD, National Geodetic Vertical Datum]

Well

Period of record

Well-screen interval (feet below land surface)

Mean depth

to water (feet below land surface)

Mean water-level elevation (feet above NGVD 29) Period of

Water year 2002

S3W184 NUW128

HZW147 225

270 271 272 273 274 275

274 275 276 277 278 279

184

186 185 187 188 189 190 191 192 193 194 186 187 188 189 190 191 153

155 154 156 157 158 159 160 161 162 163

EXPLANATION

MEASURED, 2001–02 ESTIMATED MONTHLY AVERAGE, 1997–2001

Figure 8 Measured water levels, September 2001 through December 2002, and estimated average monthly water levels,

1997–2001, at selected observation wells in the Assabet River Basin, eastern Massachusetts

Surface Water

The Assabet River originates at a large flood-control dam

and impoundment at its headwaters in Westborough (the A1

Impoundment), and is impounded by six other mill dams before

joining the Sudbury River in Concord (fig 1) Some of the

impoundments, such as that upstream of the Ben Smith Dam in

Maynard, extend for several miles The total elevation change

along the length of the river is about 200 ft and occurs mostly

at the dams and near the headwaters of the river Most major

tributaries in the basin flow from northwest to southeast and

include Hop, Cold Harbor, Howard, Stirrup, North, Danforth,

Elizabeth, Fort Pond, and Nashoba Brooks (fig 1)

Flood-control or mill dams also are common along the major

tributaries, creating reservoirs, lakes, or wetlands and in some

cases affecting main stem flow Examples include Millham

Reservoir, Fort Meadow Reservoir, Lake Boon, Delaney Pond

and surrounding wetlands, and the wetlands along Cold Harbor

and Hop Brooks (fig 1) Wetlands along small perennial and

intermittent streams also are common throughout the basin

Streamflow

Average flow in the Assabet River at the continuous

streamflow-gaging station in Maynard (0109700), with a

drainage area of about two-thirds of the basin (116 mi2), is

188 ft3/s (table 5) Average streamflow out of the basin is

an estimated 287 ft3/s (185 Mgal/d), as determined by the

drainage-area ratio method and flow at the Maynard station

Average flow at the continuous streamflow-gaging station on

Nashoba Brook (01097300), a major tributary to the Assabet

River, is 20.2 ft3/s (table 5) In addition to measurements at

the two continuous streamflow-gaging stations in the basin,

streamflow was measured at 6 partial-record sites on the main

stem Assabet River and at 13 tributary sites at monthly intervals

from May or June 2001 through December 2002 (fig 6 and

table 6; see Socolow and others, 2003, for measurement data)

Streamflow measurements were made after several days of dry

weather; therefore, they represented nonstorm streamflow

Nonstorm streamflow in tributaries is defined here as base

flow minus any surface-water withdrawals; in the main stem

Assabet River, it is base flow minus withdrawals plus

waste-water discharges Nonstorm streamflow excludes direct stream (stormwater) runoff, which occurs immediately after a precipi-tation event Like water levels, streamflows in the basin during the measurement period were lower than average, as indicated

by flows at streamflow-gaging stations in and near the basin (fig 9 and table 5)

For streamflow-gaging stations in the basin, mean annual and monthly nonstorm streamflow for 1997–2001 was calcu-lated directly from streamflow records by using the automated hydrograph-separation method, PART (Rutledge, 1993) For partial-record study sites, mean annual and monthly streamflow and nonstorm streamflow for 1997–2001 (Appendix 1) were estimated by using the MOVE.1 methods described previously for water levels The MOVE.1 analysis was done on logarithms

of flow, in the way that the method commonly is applied

to streamflow (Bent, 1995, 1999; Ries and Friesz, 2000) Instantaneous streamflow at measurement sites was correlated with same-day mean daily streamflow at up to eight nearby long-term streamflow-gaging stations (table 5) Long-term stations were on largely unregulated streams and represent ranges of drainage areas and percentages of stratified glacial deposits in drainage areas that were similar to the study sites Nonstorm streamflow, or base flow at long-term stations, was estimated by using PART The comparison between stream-flows at largely unregulated, long-term stations and at study sites assumes that flow components of nonstorm streamflow other than base flow at the study sites are of negligible quantity,

or at least have insignificant effects on the temporal variation of flows For main stem Assabet River sites where wastewater is a large and variable component of nonstorm streamflow, this assumption may introduce error, especially during low-flow months

Mean annual flows for 1997–2001 at streamflow-gaging stations were similar to long-term average flows, and much higher than (about twice) flows in water year 2002 (table 5) Estimated mean annual nonstorm streamflow was about 70 to

80 percent of total flow at all stations except for the Old Swamp River station (01105600, 60 percent of total flow), which drains

a small basin with extensive wetlands Nonstorm streamflow at the Assabet River station (01097000), which would be expected

to include most of the wastewater discharged to the river in the basin, was about 80 percent of total flow, one of the highest percentages of total flow

Table 5 Drainage-area characteristics and mean annual flows at streamflow-gaging stations in and near the Assabet River Basin,

eastern Massachusetts

[Period of record: Extends from date shown to present Estimated nonstorm streamflow: Estimated by using the automated hydrograph-separation method,

PART (Rutledge, 1993) See Socolow and others (2003) for site locations mi2, square miles; ft3/s, cubic foot per second; , not determined]

Station

Period of record

Area of stratified glacial deposits (percent)

Period of record

1997–

2001

Water year 2002

Period of record

1997–

2001

Water year 2002

01096000 Squannacook River near West

Groton, MA

01105600 Old Swamp River near South

Weymouth, MA

Wastewater in the Assabet River at Maynard station,

which averaged 9.6 Mgal/d (14.9 ft3/s) in 1997–2001, was

about 8 percent of total flow annually Some wastewater that

discharges to the river during large storms from increased

infiltration to sewers may be partitioned to the storm

stream-flow component of stream-flow by PART This component of stream-flow

would be difficult to quantify but probably was a small

percentage of the total wastewater discharge The effect of

wastewater discharge on flows in the Assabet River is indicated

by a significant upward trend with time in mean monthly

nonstorm streamflow during the low-flow period A Kendall

rank correlation of monthly flow and year for the Assabet River

showed significant relations for July, August, September, and

October (p-values equal to 0.054, 0.034, 0.029, and 0.001,

respectively) This trend was not apparent at other

streamflow-gaging stations Estimated mean monthly flows for 1997–2001

at partial-record sites (fig 10), like the

streamflow-gaging-station data and ground-water levels, were considerably higher

than instantaneous measurements in the fall of 2001 and

summer of 2002 Estimated mean monthly flows for 1997–2001

at partial-record sites peak sooner and higher than ments in the spring of 2002, with the exception that high-flow measurements in early March 2002 were affected by heavy precipitation on March 1

measure-Nonstorm streamflows, calculated with PART or other hydrograph-separation methods for a basin, are estimates that incorporate simplifying assumptions about flow in the basin Total flow is partitioned into storm and nonstorm components by applying an algorithm that is based on a simple model of streamflow recession that may not apply equally well to all seasons or various local conditions The methods also may not be able to distinguish accurately between ground-water discharge and the slow drainage of water stored in impoundments or wetlands following a short-term or seasonal streamflow peak Because of these and other considerations (DeSimone and others, 2002), streamflow components from PART and similar methods are considered to be more accurate for larger time intervals, such as years, than for shorter time intervals, such as months (Rutledge, 1993), and are always only estimates

DAILY MEAN, 1997–2001

A 01097000 ASSABET RIVER AT MAYNARD

B 01097300 NASHOBA BROOK NEAR ACTON

Figure 9 Monthly mean streamflow for long-term average conditions and daily mean streamflow, 1997–2001:

A, Assabet River streamflow-gaging station at Maynard; B, Nashoba Brook streamflow-gaging station near Acton,

Massachusetts

Ponds and Wetlands

Ponds in the Assabet River Basin include instream ponds

and impoundments, typically formed by mill or flood-control

dams, and kettle lakes, depressions in the stratified glacial

deposits that intersect the water table Many kettle lakes also

have surface-water inflows and outflows Water levels were

measured at about monthly intervals in 12 ponds and

impound-ments (fig 6 and table 3) Water levels changed little in the river

impoundments or ponds upstream of dams (instream ponds),

such as Bartlett Pond and Lake Boon (fig 11) In kettle lakes, such as Chauncy Lake and White Pond, water-level fluctuations were similar to those of ground water, although they were affected by ice conditions Average annual water levels for 1997–2001 were estimated for ponds and impoundments by using the MOVE.1 methods (table 3), but these estimates may not be meaningful for ponds and impoundments where water levels are controlled predominantly by dams and outflow structures

(01097380) ELIZABETH BROOK (01096945)

INSTANTANEOUS STREAMFLOW MEASUREMENT,

J A O N D

J

J F M A M J J A S O N D S

J A O N D

J

J F M A M J J A S O N D S

Figure 10 Instantaneous streamflow measurements, June 2001 through December 2002, and estimated mean monthly

streamflow and nonstorm streamflow at selected flow-measurement sites in the Assabet River Basin, eastern

Massachusetts

Wetlands are common in the basin, covering 3 percent

of the basin area in 1999 Wetlands include areas mapped as

bogs, marshes, shrub swamps, and forested wetlands (fig 1;

MassGIS, 2001; 1:5,000 scale) Wetlands potentially have

important but variable, and largely unknown, functions in

surface- and ground-water-flow systems at the regional scale

(Carter and Novitzki, 1988; Mitsch and Gosselink, 1993; Hunt

and others, 1996; Cole and Brooks, 2000) Their interaction

with surface and ground water varies with location in the

landscape, connection with other surface waters, and subsurface

soil and hydrogeologic conditions Wetlands commonly are

considered to store surface runoff and reduce flood peaks

Wetlands may receive ground-water inflow and drain to surface

water; they may be isolated from the ground-water system; or

when water levels in the wetland are above the surrounding water table, such as in a perched system, they may be sources

of recharge to ground water Evapotranspiration in riparian wetlands also may reduce streamflow in the summer (Motts and O’Brien, 1981) Wetlands in the Assabet River Basin, the majority of which are forested, are along all major tributaries and along the main stem river (fig 1) Wetland areas that appear isolated in figure 1 are likely connected to the surface-water-flow system by small streams that in most cases that not apparent in the smaller scale (1:25,000) stream data Because

of their position low in the landscape and flow system, most wetlands in the basin probably are predominantly in areas of ground-water discharge (Motts and O’Brien, 1981)

BARTLETT POND

LAKE BOON

CHAUNCY LAKE DELANEY POND

WHEELER POND 227

228 229 230 231 232

227 228 229 230 231 232

187 188 189 190 191 192

222 223 224 225 226

227

WHITE POND

173 174 175 176 177

178 ASSABET RIVER BEN SMITH IMPOUNDMENT

307 308 309 310 311

312 A1 IMPOUNDMENT

Figure 11 Measured water levels, September 2001 through December 2002, at selected ponds and impoundments in the

Assabet River Basin, eastern Massachusetts

Water Use and Management

Information on water use and management was collected to

quantify inflows and outflows of water from the ground- and

surface-water-flow systems in the basin Water withdrawals for

public supply, agricultural, and other uses are outflows from

the aquifers and streams After use, most of the water that is

withdrawn for these purposes is returned to ground or surface

water as wastewater Water imported for public supply from

sources outside of the basin represents an inflow when it is

discharged to ground or surface water after use Some water

is used consumptively; this water is a net outflow in areas of

private water supply and waste disposal In publicly supplied

areas, consumptive use is not a separate outflow from ground- or surface-water-flow systems, but is included in the imbalance between water withdrawals and wastewater return flows Finally, infiltration of ground water into sewers is an outflow from the ground-water-flow system When this water is discharged to streams as part of the treated wastewater from a municipal facility, it becomes an inflow to surface water Inflows and outflows to the ground- and surface-water-flow systems from water use and management are shown schematically in figure 12 Overall, water use and management in the Assabet River Basin result in a net import of water, primarily as waste-water, and a net transfer of water from ground-water to surface-water-flow systems

Septic Systems

Ground Water (-6.4)

Surface Water (+8.5)

3.7

1.7

1.5

0.3 2.2 11

7.2

0.1

3.5 0.2 0.4 0.7

All volumes in million gallons per day

1 million gallons per day

2 million gallons per day

5 million gallons per day

I/I

UNACC

PrivWUnper

Figure 12 Water use and return flows in the Assabet River Basin in eastern Massachusetts Water withdrawals and

discharges are average annual rates for 1997–2001; consumptive-use, septic-system return flow, and

unaccounted-for water are annual averages unaccounted-for 2000 I/I, infiltration to sewers; MWRA, Massachusetts Water Resources Authority;

PrivW, private-water consumptive use; PW, public-water withdrawal or consumptive use; UNACC, unaccounted-for

water; Unper, unpermitted agricultural and golf-course consumptive use; WMA, nonmunicipal permitted withdrawal

or consumptive use Positive (+) and negative (-) values are net gains and losses, respectively, from surface water and

ground water

Water Supply and Consumptive Use

Public-water systems (municipal or publicly owned

systems) supply most water users in 12 of the 20 towns in the

Assabet River Basin (table 7), serving about 80 percent of the

basin population and about half of its area (fig 13) Most

publicly supplied water is obtained from within the basin,

primarily from wells but also from several reservoirs (table 8

and fig 14) Several towns that are only partly within the basin

have water sources in the adjacent Blackstone, Concord,

Nashua, or Sudbury River Basins as well as in the Assabet River

Basin (table 9) The Massachusetts Water Resources Authority

(MWRA) also supplies water to Marlborough, Northborough,

and Clinton from sources in central Massachusetts

Public-supply withdrawals from sources in the basin

averaged 9.4 Mgal/d in 1997–2001 (table 8) Most (77 percent)

public-supply withdrawals were from ground water (fig 12),

and ground-water withdrawals for public supply were nearly all

(98 percent) from stratified glacial deposits During the study

period, total withdrawals by public-water systems in most

towns in the basin were at or near their current permitted limits

under the Massachusetts Water Management Act (WMA;

table 9) Withdrawals were greatest in May, June, and July

(fig 15) Withdrawals likely were greater in these months

because of outdoor water use, which is partly or wholly

consumptive This seasonal pattern also is apparent in per capita

water-use rates in early summer, which average 30 percent

greater than rates in November through March

Imported water for public-supply use from MWRA for

Marlborough and Northborough averaged about 1.7 Mgal/d

in 1997–2001 (fig 12) Water imported from MWRA for the

small area of Clinton in the basin is not considered in this study,

because it is disposed of outside of the Assabet River Basin

The estimate for Marlborough includes an apportionment,

based on town area in and out of the basin, of the total amount

of MWRA water supplied to Marlborough The estimate for

Marlborough may be higher than is typical because nearly all of

Northborough’s water was supplied by MWRA in 2001, which

was a temporary arrangement Most of the MWRA imported

water is delivered to wastewater-treatment facilities after use

(fig 12) Little information is available on volumes of water

imported (or exported) from sources in adjacent basins through

the public-supply water-distribution systems of the individual

towns (table 9) However, the volumes of imported or exported

water are likely to be small, except in Shrewsbury, a densely populated town in which all water used in the basin in 1997–

2001 originated in the adjacent Blackstone River Basin

In the eight towns in the basin without public-water systems (table 7), private water companies or domestic wells supply water to residential, industrial, and other users Nonmunicipal drinking-water sources are entirely from ground water, and include wells in bedrock and stratified glacial deposits Data on locations and withdrawal rates for these sources are limited; however, comparison of public-water and sewer systems (fig 13) indicates that areas without public water are not sewered Consequently, water withdrawn through private water systems and wells is returned to the aquifers through on-site disposal, except for water that is used consumptively

Consumptive use by publicly and privately supplied users was estimated from an analysis of seasonal water use in 11 publicly supplied towns (all publicly supplied towns except Clinton, for which no water-use data were collected; table 7) and land-use data For this study, consumptive use is defined as the component of a water-supply withdrawal that is removed permanently from the ground- or surface-water system, through evaporation or other processes Consumptive use was assumed

to result from irrigation or other water use during the high- use months of spring, summer, and fall Consumptive use (volumetric rates) in each month from April through October for each town was calculated as the difference between with-drawals in the month and the mean withdrawal rate in the low-use winter months of November through March Months were identified as low- or high-use months based on the seasonal patterns of public-supply withdrawals in 1997–2001 (fig 15) Areal rates were calculated by applying volumetric rates for each town to the developed land uses in publicly supplied areas

in the towns, which were identified as areas of residential, commercial, industrial, and urban public land use within the extent of public-water systems Monthly areal rates of con-sumptive water use ranged from 0.4 in/yr in April to 2.59 in/yr

in July; the mean annual rate was 0.92 in/yr These rates were applied to developed land-use areas in privately supplied towns

to estimate a mean annual consumptive use for privately supplied parts of the basin of 0.72 Mgal/d This volume is a net outflow from the ground-water system in privately supplied, developed areas (fig 16) Consumptive use in publicly supplied parts of the basin was estimated similarly at 0.71 Mgal/d

This volume is not a separate outflow from the ground- or

surface-water systems in publicly supplied areas, as mentioned

previously, because it is included in the difference between

public-water withdrawals and municipal wastewater

discharges This approach to estimating consumptive use

does not take into account any differences in population density

or land use between publicly and privately supplied areas;

therefore, consumptive use in privately supplied areas (which

are likely to be less densely populated) may be over- or

underestimated This approach also does not quantify variation

in rates of consumptive use among land uses

Withdrawals by several large industrial, agricultural, and golf-course users averaged 0.43 Mgal/d in 1997–2001 (table 8) These consist of withdrawals greater than 100,000 gal/d that are permitted under the WMA The nonmunicipal WMA withdrawals are mostly from surface-water sources, including the Assabet River, tributary streams, and ponds; wells in stratified glacial deposits and bedrock also are used (fig 12) Seasonally, these withdrawals peak in mid- to late summer, because of increased irrigation by agricultural and golf-course users Industrial uses usually are constant throughout the year

1 Value applies to area of town in basin.

2 Includes use reported as semiresidential.

Table 7 Population on public water and sewer and per capita water use in the Assabet River Basin, eastern Massachusetts, 2000.

[Total population: From U.S Census Bureau, 2003 Population on public water and sewer: From U.S Census Bureau, 2003, and town water departments

Estimated residential water use: From 2000 public water-supply statistical reports from towns to the Massachusetts Department of Environmental Protection Estimated per capita use in summer: Average use in May, June, and July Estimated per capita use in winter: Average use from December through March

gal/person/d, gallons per person per day; Mgal/d, million gallons per day; , not determined]

Town

Proportion

of town

in basin (percent)

Total population

Population on public water and sewer (percent)

Estimated public-supply residential water use (Mgal/d)

Estimated per capita use (gal/person/d)

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS From USGS and MassGIS data sources, Massachusetts State Plane

Coordinate System, Mainland Zone

EXPLANATION

TILL OR BEDROCK STRATIFIED GLACIAL DEPOSITS

BASIN BOUNDARY TOWN BOUNDARY PUBLIC-WATER DISTRIBUTION LINE SEWER LINE MUNICIPAL WASTEWATER DISCHARGE

71 o 36'

Figure 13 Public-water and sewer systems in the Assabet River Basin, eastern Massachusetts.

Table 8 Permitted water-supply withdrawals and wastewater discharges in the Assabet River Basin, eastern Massachusetts

[Identifier: See figure 14 for locations Source type: GWSG, ground water, stratfied glacial deposits; GWB, ground water, bedrock; SW, surface water

Subbasin: MS, Main stem; Head, Headwaters Maximum permitted withdrawal rate: Data from B.R Bouck, Massachusetts Department of Environmental

Protection, written commun., 2003; rates for industrial, agricultural, and golf-course sources are mean annual rates No., number; Mgal/d, million gallons per day; , not applicable or not known]

type

Well depth (feet)

Mean annual withdrawal or discharge rate, 1997–2001 (Mgal/d)

Maximum permitted withdrawal rate (Mgal/d)

Public-Supply Withdrawals

MN-01G Maynard Old Marlborough Road Well

MN-04G Maynard Rockland Avenue Wells Nos 2,

3, and 5

470

NB-03G Northborough Crawford Street Well Cold Harbor and

1 Withdrawals are pumped to ML-01S.

2 Includes two wells and a reservoir.

3 Maximum permitted withdrawal rate is combined rate for INT-01G and INT-02G.

4 Maximum permitted withdrawal rate is combined rate for SCC-01S, SCC-02S, and two other sources that were unused in 1997–2001.

Public-Supply Withdrawals—Continued

Industrial, Agricultural, and Golf-Course Withdrawals

SW

Wastewater Discharges

MLW-WWTF Marlborough Westerly Wastewater-

Treatment Facility

WB-WWTF Westborough Regional Wastewater-

Treatment Facility

Table 8 Permitted water-supply withdrawals and wastewater discharges in the Assabet River Basin, eastern

Massachusetts.—Continued

[Identifier: See figure 14 for locations Source type: GWSG, ground water, stratfied glacial deposits; GWB, ground water, bedrock; SW, surface water

Subbasin: MS, Main stem; Head, Headwaters Maximum permitted withdrawal rate: Data from B.R Bouck, Massachusetts Department of Environmental

Protection, written commun., 2003; rates for industrial, agricultural, and golf-course sources are mean annual rates No., number; Mgal/d, million gallons per day;

type

Well depth (feet)

Mean annual withdrawal or discharge rate, 1997–2001 (Mgal/d)

Maximum permitted withdrawal rate (Mgal/d)

TILL OR BEDROCK STRATIFIED GLACIAL DEPOSITS

BASIN AND SUBBASIN BOUNDARY PUBLIC-SUPPLY SOURCE

AND IDENTIFIER PERMITTED INDUSTRIAL, AGRICULTURAL, OR GOLF- COURSE SOURCE AND IDENTIFIER

WASTEWATER DISCHARGE AND IDENTIFIER

0 1 2 3 4 5 KILOMETERS From USGS and MassGIS data sources, Massachusetts State Plane

Coordinate System, Mainland Zone

NB-04G

GRK-01S

JUN-01S NB-01G

WB-05G,-06G WB-03G

WB-WWTF NB-02G

BIG-01S

NB-03G

MLW-WWTF

CNS-01S HD-01S

WB-04G

HD-03G HD-02G HD-WWTF

WWTF MID-WWTF

MCI-MN-01S HD-04G

HD-01G

MN-01G SCC-01S

AN-10G

AN-02G CN-01S

AN-01G

HD-WWTF ASG-01G

WB-02G WB-01G

BER-01S

WB-07G

ML-01S ML-02S

INT-02G

HD-05G

MN-02G MN-WWTF

AN-01G AN-07G

AN-09G

AN-11G

AN-04G AN-08G AS-06G

Table 9 Existing (1997–2001) and permitted withdrawals for

municipal public-water systems in the Assabet, Sudbury, and Concord River Basins, eastern Massachusetts

[Basin location of public-water sources: A, Assabet; S, Sudbury, C, Concord

Maximum permitted withdrawals: From Duane LeVangie, Massachusetts

Department of Environmental Protection, written commun., 2002; rates are system-average annual rates permitted under the Massachusetts Water Management Act for withdrawals in the Assabet, Concord, and Sudbury River Basins Mgal/d, million gallons per day]

Town

Basin location of public- water sources

Total mean annual withdrawals for public supply (Mgal/d)

Maximum permitted withdrawals (Mgal/d)

PUBLIC WATER SUPPLIED BY MASSACHUSETTS

WATER-RESOURCES AUTHORITY WASTEWATER DISCHARGES

EXPLANATION

MONTH

Figure 15 Monthly average permitted withdrawals, wastewater discharges, and imported water for public supply, 1997–

2001, in the Assabet River Basin, eastern Massachusetts

AREA OF CONSUMPTIVE USE

IN PRIVATE-SUPPLY AREAS TILL OR BEDROCK

TOWN BOUNDARY

BASIN AND SUBBASIN BOUNDARY

AREA OF SEPTIC-SYSTEM RETURN FLOW IN PUBLIC- SUPPLY AREAS

STRATIFIED GLACIAL DEPOSITS

0 1 2 3 4 5 KILOMETERS From USGS and MassGIS data sources, Massachusetts State Plane

Coordinate System, Mainland Zone

Figure 16 Areas of private-water supply with consumptive water use and areas of public-water supply with septic-system

return flow in the Assabet River Basin, eastern Massachusetts

Withdrawals by small and large agricultural and

golf-course users in the Assabet River Basin are generally

considered to be entirely consumptive (Barbara Kickham,

Massachusetts Department of Environmental Protection,

written commun., 2003) Data on water withdrawals by the

large, permitted agricultural users were used to estimate

consumptive use by the small, unpermitted users in privately

supplied areas Small agricultural users were identified as

areas mapped in 1999 land-use data as nurseries and cropland

Mean annual consumptive use for nursery (0.04 mi2) and

cropland (3.2 mi2) areas in the basin were estimated at 0.02 and

0.24 Mgal/d, respectively Consumptive use by unpermitted

golf-course withdrawals was estimated from application

rates listed in the MADEP golf course water-use policy

(Massachusetts Department of Environmental Protection,

2000) and the irrigated area of four unpermitted golf courses in

the basin (Barbara Kickham, Massachusetts Department of

Environmental Protection, written commun., 2003) Water use

for agriculture and golf courses is seasonal, with maximum use

in summer Monthly mean rates of cropland use were estimated

at 0.96 Mgal/d in June, July, and August; rates for nurseries

ranged from 0.02 Mgal/d in November to 0.07 Mgal/d in

July; and unpermitted golf-course withdrawals ranged from

0.008 Mgal/d in April to 0.22 Mgal/d in June, July, and August

Mean annual consumptive use by unpermitted golf courses

in the basin was estimated at 0.08 Mgal/d The unpermitted

withdrawals may be from either surface water or ground water,

but are shown as surface-water withdrawals in figure 12

Wastewater Discharge and Return Flow

Municipal water-treatment facilities in Westborough,

Marlborough, Hudson, and Maynard discharge treated

waste-water into the Assabet River (fig 14) These facilities treat

wastewater from about 50 percent of the basin population, in

eight towns Additionally, wastewater from the MCI Concord

prison facility is discharged to the Assabet River, and

waste-water from Middlesex School in Carlisle is discharged to

Spencer Brook (table 8) Total wastewater discharges averaged

11.0 Mgal/d in 1997–2001 Discharges from the four municipal

facilities included water withdrawn from sources in and out of

the basin: wastewater from Shrewsbury that originated from

sources in the Blackstone River Basin is treated and discharged

at the Westborough facility, and wastewater that was imported

from MWRA is discharged at the Marlborough facility The

Marlborough facility also treats and discharges wastewater

from Northborough (about 15 percent of total flows), but

this water originated at sources in the Assabet River Basin

Seasonally, wastewater discharges are greatest in February,

March, and April (fig 15) Soils are saturated and the water table is high, so that infiltration of ground water to sewers is greatest during these months

Wastewater from unsewered areas is returned to the ground-water-flow system through on-site septic systems Areas receiving septic-system return flow as a net inflow to the ground-water system were identified as areas of developed land use within public-water systems that were beyond the extent of existing sewer systems (fig 13) The rates and spatial distribu-tion of septic-system return flow from residential water use was estimated from per capita water use, land use, and population data Population densities per residential land-use type (multi-family residential, and high-, medium-, and low-density residential) were estimated from multiple regression of total population by town and area of each land-use type Population densities determined by the regression were adjusted so that total population for each town equalled census data for year

2000 Septic-system return flow rates for residential areas were calculated by using the adjusted population densities and

an average rate of nonconsumptive per capita water use for publicly supplied towns, about 60 gal/person/d (winter water-use rate; table 7) Return flow rates from water use in commercial, industrial, and urban public land-use areas were calculated from data on the number of employees per town per Standard Industrial Classification (SIC) Code for 2000 (Massachusetts Division of Employment and Training, 2003) and typical values of water use per employee per SIC code (Horn, 2000) Total commercial, industrial, and urban public water use was estimated for each town, and then apportioned to the study area by using the percentage of town area in the basin Septic-system return flow rates thus calculated for land-use categories averaged 1.2 in/yr for low-density residential, 4.8 in/yr for medium-density residential, 10 in/yr for high-density residential, 33 in/yr for multi-family residential, and

13 in/yr for commercial, industrial, and urban public land use; the rates were assumed to be constant throughout the year Summed across the entire study area, septic-system return flow was 4.34 Mgal/d, about 20 percent of which originated from water-supply sources outside of the basin (fig 12)

Finally, infiltration to sewers is an outflow from the ground-water-flow system that can be estimated with informa-tion from the Wastewater Management Plans of towns in the Assabet Consortium Infiltration to sewers was reported, as fractions of total wastewater flows, at 27 percent for Hudson, 32 percent for Marlborough, 26 percent for Maynard, 37 percent for Northborough, and 17 percent for Westborough and Shrewsbury (Camp, Dresser and McKee, 2002; Dufresne-Henry, 2001; Earth Tech, 2001e, 2002d; Fay, Spoffard, & Thorndike, 2001a) Rates vary seasonally, with maximum